TOEFL iBT Reading Practice Test- Lesson 2

Read this paragraph and answer the following questions

One of the factors in global warming is carbon monoxide. The more carbon monoxide in the atmosphere, the less the atmosphere is able to clean itself. The result is a warming of the atmosphere, the so-called global warming, and possibly ozone damage.
5 Earlier, it was found that carbon monoxide was concentrated in the Southern Hemisphere, and could be attributed to deforestation. Huge areas of forest and grasslands in South America and Africa have been burned, putting carbon monoxide into the atmosphere. Recently, however, 10 the Southern Hemisphere has been found to be clean, while the Northern Hemisphere is more polluted than expected.

The latest research was done during the northern winter. The high levels in the Northern Hemisphere could be because of this. In winter 15 carbon monoxide is destroyed more slowly. There are also more fires burned in winter, and possibly industrial processes work harder. It could also reflect the ever-increasing number of cars on the roads. Optimists hope that the reason why the North has overtaken the South as the major area of carbon monoxide is that at last the burning 20 has stopped, or at least slowed down.